Hemorrhagic septicemia in the United States: molecular characterization of isolates and comparison to a global collection.

Hemorrhagic septicemia-causing strains of Pasteurella multocida are endemic in Asia and Africa, but naturally occurring hemorrhagic septicemia has not been described in livestock in the United States since 1993. There are 5 capsular types of P. multocida: A, B, D, E, and F. Two capsular types (B, E) cause hemorrhagic septicemia, whereas capsular types A and, to a lesser extent, D are associated with enzootic bovine pneumonia. Here we describe 2 naturally occurring cases of hemorrhagic septicemia caused by P. multocida capsular type B:3,4 in the United States, including molecular characterization of these strains, with a comparison to available reference strains and publicly available genomes of P. multocida capsular type B. Genomic analyses demonstrated that our case strains are similar to a strain isolated from New Jersey cattle in 1968 and to contemporaneous strains from New Zealand and Canada. These strains are different from those circulating globally, as demonstrated by the need to assign new sequence types for our isolates. Hemorrhagic septicemia appears to be re-emerging globally in countries that have not seen outbreaks in decades and may be poised for re-emergence in the United States given the identification of these novel strains.